In the 3rd generation partnership project long term evolution (3GPP LTE) system, the uplink power control is used for controlling the transmission power of the uplink physical channel, so as to compensate the path loss and shadow fading of the channel, and suppress inter-cell interference. The uplink physical channels controlled by the uplink power control comprise the physical uplink shared channel (PUSCH), the physical uplink control channel (PUCCH) and sounding reference signal (SRS). The uplink power control of LTE adopts the combined control mode of open loop and closed loop.
In the LTE system, the transmission power of PUSCH of user equipment (UE) on the subframe i is defined as:PPUSCH(i)=min{PCMAX,10 log10(MPUSCH(i))+PO—PUSCH(j)+α(j)·PL+ΔTF(i)+f(i)}[dBm]
in which, PCMAX is the configured maximum UE output power, the range of which is jointly determined by the maximum UE power determined by the UE power class, the IE P-Max configured by system, the configured maximum output power tolerance (PCMAX tolerance), and the maximum power reduction (MRP) and the additional maximum power reduction (A-MPR) which are caused by the operation frequency band, the system bandwidth, the modulation order, the transmission bandwidth position, the transmission bandwidth configuration and so on;
P′PUSCH(i))=10 log10(MPUSCH(i))+PO—PUSCH(j)+α(j)·PL+ΔTF(i)+f(i) is the transmission power of PUSCH which is estimated by the UE according to the open loop and closed loop power control parameters and instructions of base station, the path loss estimate, and the number of resource blocks of PUSCH sent on the subframe i;
MPUSCH(i) is the bandwidth of PUSCH transmission on the subframe i, which is represented by the number of resource blocks (RBs);
PO—PUSCH(j) is an open loop power control parameter, which is the sum of a cell specific value PO—NOMINAL—PUSCH(j) and a UE specific value PO—UE—PUSCH(j); in which, j=0 corresponds to the semi-persistent scheduled PUSCH transmission, j=1 corresponds to the dynamic scheduled PUSCH transmission, and j=2 corresponds to the random access response scheduled PUSCH transmission (the PUSCH transmission scheduled by the random access response);
α is the cell specific path loss compensation factor. When j=0 or 1, α(j)ε{0, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1}, and when j=2, α(j)=1. α=1 is the complete path loss compensation, and α<1 is the partial path loss compensation;
PL is the downlink path loss estimate which is measured and computed at UE;
ΔTF(i) is a power offset related to the modulation coding scheme (MCS); and
f(i) is the current power control adjustment state of PUSCH. According to the configuration of higher layer parameter, in the case of the accumulated value power control, f(i)=f(i−1)+δPUSCH(i−KPUSCH)) and in the case of the absolute value power control, f(i)=δPUSCH(i−KPUSCH). δPUSCH is a UE specific closed loop correction value, which is also called transmission power control (TPC) command.
In the LTE system, the transmission power of PUCCH of UE on the subframe i is defined as:PPUSCH(i)=min{PCMAX,P0—PUCCH+PL+h(nCQI,nHARQ)+ΔF—PUCCH(F)+g(i)}[dBm]
in which, the definition of PCMAX is same as what mentioned above;
P′PUCCH(i)=P0—PUCCH+PL+h(nCQI,nHARQ)+ΔF—PUCCH(F)+g(i) is the transmission power of PUCCH which is estimated by the UE according to the open loop and closed loop power control instructions of base station, the path loss estimate, and the PUCCH format sent on the subframe i;
PO—PUCCH is an open loop power control parameter, which is the sum of a cell specific value PO—NOMINAL—PUCCH and a UE specific value PO—UE—PUCCH;
ΔF—PUCCH(F) is a power offset related to the PUCCH format (F), which is configured by the higher layer;
h(n) is a value based on the PUCCH format (F), in which, nCQI is the information bit number of CQI, and nHARQ is the bit number of HARQ; and
g(i) is the current power control adjustment state of PUCCH,
      g    ⁡          (      i      )        =            g      ⁡              (                  i          -          1                )              +                  ∑                  m          =          0                          M          -          1                    ⁢                                    δ            PUCCH                    ⁡                      (                          i              -                              k                m                                      )                          .            δPUCCH is a UE specific closed loop correction value, which is also called transmission power control (TPC) command.
It has to be noted that in the LTE system, in order to maintain the single-carrier character of uplink signal, for the same UE, the PUSCH and the PUCCH cannot be transmitted at the same time.
To make the base station know the margin between the configured maximum output power which is set by some UE at certain time and the estimated transmission power of PUSCH which is scheduled by the base station, so as to allow the base station to know whether the UE is limited in power, providing the basis for the base station to schedule resource scheduling and link adaptation of PUSCH for the next time, and schedule suitable modulation coding scheme and bandwidth for UE, and the UE needs to measure the power headroom (PH) of itself and reports it to the base station. In the LTE system, the power headroom of a certain UE on the subframe i is defined as:PH(i)=PCMAX−{10 log10(MPUSCH(i))+PO—PUSCH(j)+α(j)·PL+ΔTF(i)+f(i)}[dB]
which is the difference between the configured maximum output power set by UE and the transmission power of PUSCH estimated by UE. The power headroom which is obtained by measuring and computing is quantized within the range of [40,−23] dB, to the extent of 1 dB as precision (the quantification relationship is shown in Table 1), and then is transferred to the higher layer by the physical layer. The media access control layer (called MAC layer for short) uses 6 bits index to represent the quantized power headroom. The mapping relationship is shown in Table 1, and the 6 bits index is also called power headroom.
In addition, the power headroom report (PHR) is event-triggered. When the UE has new PUSCH transmission on the current subframe, there is event triggering the PHR, and the channel resource which the base station assigns for the PUSCH transmission of the UE is, according to a certain priority of logical channels, enough to bear the power headroom MAC control element and MAC protocol data unit (PDU) sub-header thereof, the UE reports the 6 bits power headroom to the base station through the power headroom MAC control element.
The structure of the power headroom MAC control element is shown in FIG. 1. It is an octet, in which the highest 2 bits are reservation bits (R) set as 0, and the low 6 bits are the reported power headroom (PH).
It has to be noted that in the LTE system, only the power headroom of the subframes which transmit the PUSCH is measured.
TABLE 1diagram of quantification and report mapping of power headroomPHpower headroom levelmeasured quantification value (dB)0POWER_HEADROOM_0−23 ≦ PH < −221POWER_HEADROOM_1−22 ≦ PH < −212POWER_HEADROOM_2−21 ≦ PH < −203POWER_HEADROOM_3−20 ≦ PH < −194POWER_HEADROOM_4−19 ≦ PH < −185POWER_HEADROOM_5−18 ≦ PH < −17. . .. . .. . .57POWER_HEADROOM_5734 ≦ PH < 3558POWER_HEADROOM_5835 ≦ PH < 3659POWER_HEADROOM_5936 ≦ PH < 3760POWER_HEADROOM_6037 ≦ PH < 3861POWER_HEADROOM_6138 ≦ PH < 3962POWER_HEADROOM_6239 ≦ PH < 4063POWER_HEADROOM_63PH ≧ 40
The LTE-Advanced system (called LTE-A system for short) is the next generation evolution system of the LTE system. As shown in FIG. 2, the LTE-A system adopts the carrier aggregation technology to expand the transmission bandwidth. Each aggregate carrier is called a “component carrier”. Multiple component carries can be continuous or discontinuous, and can be in the same operating band or different operating bands.
In the LTE-A system, the user equipment can transmit PUSCH on one (uplink) component carrier, and also can simultaneously transmit multiple PUSCHs on multiple (uplink) component carriers; and one or multiple PUCCHs can be transmitted on one (uplink) component carrier. In addition, it is proposed in the research of PUCCH in the LTE-A system that the PUSCH and the PUCCH are simultaneously transmitted on one (uplink) component carrier.
Therefore, how to measure and report the power headroom in the LTE-A system which adopts the carrier aggregation becomes a problem to be promptly solved